1. Technical Field
The present document relates to illumination systems. In particular, the present document relates to a method and system for controlling the illumination state of solid state lighting devices such as LED or OLED assemblies.
2. Background
For many decades GLS (General Lighting Service) or incandescent lamps have been the first choice for illumination in residential applications. These light sources could easily be dimmed using so called phase-cut dimmers. This has led to a large installed base of such wall dimmers. These dimmers are designed to work on relatively large loads with a substantial effective power over apparent power.
New types of light sources like CFL (Compact Fluorescent Lamp) or LED lamps offer very small loads (typical a factor of 10 less than the equivalent GLS lamp) in combination with a highly nonlinear behavior and a large capacitive impedance due to the presence of EMI (Electro-Magnetic Interference) filter networks. Due to these aspects, LED based lamp and CFL assemblies cannot be dimmed inherently using existing phase-cut dimmers. With advanced electronics it is possible to emulate dimming functionality. However, due to technical/physical limitations the dimming range as well as the range of supported dimmers and configurations in terms of the number and mix of parallel lamps operated with a particular dimmer is limited.
The present document is directed at overcoming these limitations and at fully exploiting the very excellent dimmability and controllability of LED based lamps. The method and apparatus described in the present document enable dimming of LEDs in all kinds of applications and with all kinds of dimmers of the installed base. Furthermore, the described method and apparatus allow for dimming between 100% and (almost) 0%.
With the changeover from GLS lamps and discharge lamps, mainly fluorescent lamps, to solid state lamps the controllability of such lamps extends from setting a defined light output intensity to changing the intensity at each wavelength which is emitted by the light source. This includes setting a particular colour in the emitted light or changing the so called colour correlated temperature CCT which is a measure if the light is perceived as “warm” or “cold”. In general in this document the term “dimming” is used for setting the total light or lumen intensity as well as for setting the power of individual spectral segments, while keeping the overall light output constant and in this way changing the radiated spectrum.
The particular configuration of the radiated light at a given point in time may be referred to as the illumination state.